Thin Cavity Fluidic Heat Exchanger

ABSTRACT

A heat exchanger comprising a first surface, a second surface, and a spacer configured to maintain a cavity between the first surface and the second surface, wherein the cavity has a thickness less than or equal to about 20 thousands of an inch (mils) and has a width-to-thickness ratio greater than or equal to about 8:1, and wherein the cavity allows any fluid in the cavity to exchange heat with the first surface, the second surface, or both is disclosed. Also disclosed is an apparatus comprising a thermal load and a heat exchanger substantially adjacent to or integrated with the thermal load, wherein any fluid flowing through the heat exchanger has a velocity greater than or equal to about 20 feet per second (fps).

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Heat exchangers may be used in various types of applications, such as electronic devices, refrigeration, air conditioning, space heating, and chemical processing. Heat exchangers allow heat to be transferred from a hot component to a cooler component. These components may include solids, fluids (i.e., liquids or gases), or combinations thereof. Heat exchangers may include fins, fans, and other devices, which may increase the heat transfer rate between the two components.

Heat sinks are a type of heat exchanger that is commonly used for cooling small components, such as electronic devices, microprocessors, and power handling semiconductors. Generally, heat sinks are made of metals with high thermal conductivity and may comprise a plurality of fins that increase the surface area from which heat can be diffused, thereby increasing the heat transfer rate. A fan or other forced convection source may blow air across the fins to further improve the heat transfer rate. The heat transfer performance of a heat exchanger, such as a heat sink, can be quantified in terms of thermal resistance. Accordingly, a heat sink with reduced thermal resistance may exhibit improved heat transfer performance as compared with heat sinks with higher thermal resistances. However, the heat transfer performance of heat sinks is dependent on the amount of surface area that the heat sinks have to diffuse the absorbed heat. Such dependencies can reduce or limit improvements in heat transfer performance in some applications, such as small-scale technologies or compact designs.

SUMMARY

In one embodiment, the disclosure includes a heat exchanger comprising a first surface, a second surface, and a spacer configured to maintain a cavity between the first surface and the second surface, wherein the cavity has a thickness less than or equal to about 20 thousands of an inch (mils) and has a width-to-thickness ratio greater than or equal to about 8:1, and wherein the cavity allows any fluid in the cavity to exchange heat with the first surface, the second surface, or both.

In another embodiment, the disclosure includes an apparatus comprising a thermal load and a heat exchanger substantially adjacent to or integrated with the thermal load, wherein any fluid flowing through the heat exchanger has a velocity greater than or equal to about 20 feet per second (fps).

In yet another embodiment, the disclosure includes a heat exchanger configured to implement a method comprising passing a fluid having a first temperature through a cavity at least partially defined by a surface having a second temperature, wherein the cavity substantially reduces or eliminates the heat transfer boundary layer of the fluid.

These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a cross-section view of an embodiment of a thin cavity fluidic heat exchanger (TCFHE).

FIG. 2 is a cross-section view of another embodiment of the TCFHE.

FIG. 3A is a perspective view of another embodiment of the TCFHE.

FIG. 3B is an exploded view of the TCFHE shown in FIG. 3A.

FIG. 3C is an inverted exploded view of the TCFHE shown in FIG. 3A.

FIG. 4A is a perspective view of another embodiment of the TCFHE.

FIG. 4B is an exploded view of the TCFHE shown in FIG. 4A.

FIG. 4C is an inverted exploded view of the TCFHE shown in FIG. 4A.

FIG. 5A is a perspective view of another embodiment of the TCFHE.

FIG. 5B is an exploded view of the TCFHE shown in FIG. 5A.

FIG. 5C is an inverted exploded view of the TCFHE shown in FIG. 5A.

FIG. 6A is a perspective view of another embodiment of the TCFHE.

FIG. 6B is an exploded view of the TCFHE shown in FIG. 6A.

FIG. 6C is an inverted exploded view of the TCFHE shown in FIG. 6A.

FIG. 7A is a perspective view of another embodiment of the TCFHE.

FIG. 7B is an exploded view of the TCFHE shown in FIG. 7A.

FIG. 7C is an inverted exploded view of the TCFHE shown in FIG. 7A.

FIG. 8A is a perspective view of another embodiment of the TCFHE.

FIG. 8B is an exploded view of the TCFHE shown in FIG. 8A.

FIG. 8C is a perspective cross-section view of the TCFHE shown in FIG. 8A.

FIG. 8D is a perspective cross-section view of the inlet port shown in FIG. 8A.

FIG. 9 is a schematic view of a plurality of TCFHEs implemented in an enterprise.

FIG. 10 is a schematic view of the TCFHE experimental apparatus.

FIG. 11 is a chart illustrating thermal resistance of the TCFHE for a plurality of air flowrates and cavity thicknesses.

FIG. 12 is a chart illustrating the cavity air pressure drop of the TCFHE for a plurality of air flowrates and cavity thicknesses.

FIG. 13 is a chart illustrating the thermal resistance of the TCFHE for a plurality of pneumatic power settings and cavity thicknesses.

FIG. 14 is a chart illustrating the load temperature of the TCFHE for a plurality of air flowrates and cavity thicknesses.

FIG. 15 is a chart illustrating the air outlet temperature of the TCFHE for a plurality of load temperatures and cavity thicknesses.

FIG. 16 is a chart illustrating the cavity air velocity of the TCFHE for a plurality of air flowrates and cavity thickness.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

A heat transfer boundary layer exists between a still or flowing fluid (gas or liquid) and solid surface that have different temperatures. The boundary layer exists regardless of whether the fluid is experiencing laminar or turbulent flow. The boundary layer is where the heat transfer between the fluid and the solid surface actually takes place. In other words, any fluid not within the boundary layer is not involved in heat transfer with the solid surface. Thus, the boundary layer acts as a pseudo-insulator for the remainder of the fluid (e.g. the fluid not in the boundary layer). The rate of heat transfer between the fluid and the solid surface may be quantified as thermal resistance, Θ (measured in ° Celsius per Watt (° C./W)), which may be calculated by:

Θ=x/(K*A)

where x is the thickness of the boundary layer in inches, K is the heat transfer coefficient (0.007 W/in-° C. for still air), and A is the surface area of the solid surface in square inches.

Theoretically, the amount of fluid that is located outside of the boundary layer may be reduced by reducing fluid height perpendicular to the boundary layer. For example, if the solid surface extends in the x and y directions of a Cartesian coordinate plane, then the height of fluid in the z direction could be reduced, e.g. by using another surface parallel to the solid surface. However, reducing the fluid height perpendicular to the solid surface also reduces the height of the boundary layer. Conventional wisdom suggests that reduced heat transfer rates would be expected from smaller boundary layers. While such may be true in many instances, the reverse actually occurs at small gap thicknesses. Without wishing to be limited by theory, it is believed that the fluid height can be reduced to the point that the boundary layer is substantially eliminated, at which point the heat transfer rate actually increases.

Disclosed herein is a thin cavity fluidic heat exchanger (TCFHE). The TCFHE may comprise a first surface, a second surface, and a cavity positioned therebetween. In an embodiment, the first surface is a heat transfer plate and the second surface is a cover plate. Alternatively, one of the surfaces can be a thermal load. The cavity thickness may be maintained by a spacer, which may be a gasket or an offset from the first surface or the second surface. The cavity is configured to allow a fluid, such as air, to flow therethrough and exchange heat with the first surface, the second surface, or both. An inlet port and an outlet port may be coupled to the first surface, the second surface, the spacer, or combinations thereof to promote the flow of fluid through the cavity. The cavity is configured to substantially eliminate the heat transfer boundary layer, thereby improving the heat transfer rate between the fluid and the first and/or second surfaces. The TCFHE may eliminate the need for heat sinks and/or fins. The TCFHE also allows heat to be transported from a remote location to the thermal load and/or away from the thermal load to another remote location.

FIG. 1 illustrates a cross-section view of an embodiment of a TCFHE 100. The TCFHE 100 may comprise a thermal load 170, a heat transfer plate 110, a cover plate 130, a spacer 140, a cavity 120, an inlet port 150, and an outlet port 160. These components may be assembled together as shown in FIG. 1, and are described in further detail below. Although the thermal load 170, the heat transfer plate 110, the cover plate 130, the spacer 140, and the cavity 120 shown in FIG. 1 are substantially planer, these components may have other geometries, such as cylindrical, spherical, or other geometries.

The thermal load 170 may comprise any apparatus or substance that produces or requires heat. Specifically, the thermal load 170 may be an apparatus or may be a solid, a liquid, or a gaseous compound. The thermal load 170 may be thermally coupled to the heat transfer plate 110, and as such may be heated or cooled, as appropriate, by the heat transfer plate 110. Alternatively, the heat transfer plate 110 may be integrated into a surface of the thermal load 170. The thermal load 170 may be part of a small or micro-scale device, such as an Integrated Circuit (IC), printed circuit boards (PCB), or the like. Alternatively, the thermal load 170 may be part of a mid or large-scale device, such as an air conditioner, a heater, a refrigerator, a cooling tower, or the like. In some embodiments, the thermal load 170 may be part of a power converter, such as an engine, a motor, a generator, a compressor, a transformer, a lighting system, and the like. In any event, the thermal load 170 may be a component used in a variety of applications and industries, such as the defense, power generation and distribution, automotive, chemical, and biomedical industries.

The cavity 120 may be defined by the heat transfer plate 110, the spacer 140, and the cover plate 130, which may be separate components or integrated together. The heat transfer plate 110 may be a plate or similar component that exchanges heat with the thermal load 170 and the fluid in the cavity 120. The cover plate 130 may be a plate or similar component that defines one side of the cavity 120, opposes the heat transfer plate 110, and may or may not exchange heat between another thermal load and the fluid in the cavity 120. The spacer 140 may be configured to maintain a specified distance between the heat transfer plate 110 and the cover plate 130, thereby defining the thickness of the cavity 120. The spacer 140 may be a separate component from the heat transfer plate 110 and the cover plate 130, such as a gasket. Alternatively, the spacer 140 may be part of the heat transfer plate 110 and/or the cover plate 130, such as a protrusion or offset from the heat transfer plate 110 and/or the cover plate 130. In some embodiments, the surface of the heat transfer plate 110, the cover plate 130, or both, may be roughened, corrugated, or both. Additionally or alternatively, the cavity 120 (or one of the manifolds if the TCFHE 100 is so equipped) may be filled with a porous material to further improve the heat transfer performance.

In many embodiments, the dimensions of the cavity 120 will be governed by size limitations imposed on the TCFHE 100, such as the length and width of a single IC or PCB. However, when such is not the case, the dimensions of the cavity 120 may be configured to achieve the desired heat transfer properties. For example, the thickness of the cavity 120 may be defined by the density, viscosity, velocity, and other inherent or desired properties of the fluid. Specifically, the cavity 120 thickness may be configured such that the heat transfer boundary layer between the heat transfer plate 110 and the fluid is substantially reduced or eliminated. In embodiments, the cavity 120 may have a thickness of no more than about 100 thousands of an inch (mils), no more than about 50 mils, no more than about 20 mils, no more than about 10 mils, no more than about 5 mils, no more than about 4 mils, no more than about 3 mils, no more than about 2 mils, or no more than about 1 mil. In other embodiments, the cavity 120 may have a thickness of no more than about 10 micrometers (microns), no more than about 5 microns, no more than about 1 micron, or no more than about 0.5 microns. In an embodiment, the thickness of the cavity 120 may be substantially uniform throughout the cavity 120. Alternatively, the thickness of the cavity 120 may not be substantially uniform such that the cavity increases or decreases in thickness from the inlet port 150 to the outlet port 160. Such may be designed to change with the expected fluid temperature change, if desired.

In addition, the length of the cavity 120 may be configured based on the expected temperature change of the fluid. Specifically, the length of the cavity 120 may be configured such that the fluid temperature achieves a temperature within a desired range of the heat transfer plate 110 temperature. For example, the length of the cavity 120 may be configured such that the fluid temperature achieves a temperature within about 25° C. of, within about 10° C. of, within about 5° C. of, within about 1° C. of, or about equal to the heat transfer plate 110 temperature. Alternatively, the length of the cavity 120 may be configured such that the fluid temperature is within a desired percentage of the heat transfer plate 110 temperature. For example, the length of the cavity 120 may be configured such that the fluid temperature is within about 25 percent, within about 10 percent, within about 5 percent, or within about 1 percent of the heat transfer plate 110 temperature.

Finally, the width of the cavity 120 may be configured based on the desired heat transfer rate. Specifically, given the thickness and length of the cavity 120, the width of the cavity 120 may be configured such to achieve a desired heat transfer rate between the fluid and the heat transfer plate 110. For example, the width of the cavity 120 may be configured such that the heat transfer rate is at least about 5 Watts (W), at least about 10 W, at least about 30 W, or at least about 50 W. It will also be appreciated that given additional knowledge of the TCFHE 100, such as the expected heat output of the thermal load, other thermal properties such as the thermal resistance may be calculated. The thickness, width, and/or length of the cavity 120 may also be designed based on such properties.

In some embodiments, the cavity 120 cross-sectional area may be a concern. For example, the cavity 120 cross-sectional area may be less than, about equal to, or greater than the cross-sectional area of any inlet and/or outlet tubes connected to the TCFHE 100. Specifically, it may be desirable to have the cross-sectional area of the cavity 120 be about equal to the cross-sectional area of the inlet and outlet tubing so that the fluid flowrate through the TCFHE 100 is substantially the same as the fluid flowrate through the tubing. Alternatively or additionally, the cavity 120 cross-sectional area may be configured to position a significant amount of the fluid against the relevant heat transfer surface. For example, the cavity 120 may have a width-to-thickness ratio of at least about 1:1, at least about 5:1, at least about 8:1, at least about 10:1, or at least about 100:1. In many cases, the cavity 120 may have a width-to-thickness ratio from about 100:1 to about 1,000:1, but should not be limited to such a range.

The flow of fluid through the cavity 120 may be promoted by the inlet port 150 and the outlet port 160. Specifically, the inlet port 150 may allow a fluid to flow into the cavity 120, and may be coupled to the heat transfer plate 110, the spacer 140, the cover plate 130, or combinations thereof. If desired, the TCFHE 100 may be equipped with an inlet manifold that assists in the diffusion of fluid from the inlet port 150 into the cavity 120. Similarly, the outlet port 160 allows a fluid to flow out of the cavity 120, and may be coupled to the heat transfer plate 110, the spacer 140, the cover plate 130, or combinations thereof. If desired, the TCFHE 100 may be equipped with an outlet manifold that assists in the collection of fluid from the cavity 120 into the inlet port 150. In a specific embodiment, the inlet port 150 and the outlet port 160 may be substantially perpendicular to the cavity 120, the heat transfer plate 110, the spacer 140, and/or the cover plate 130. Alternatively, the inlet port 150 and/or the outlet port 160 may be mounted at an angle, such as about 0 degrees, about 30 degrees, about 45 degrees, or about 60 degrees with respect to the cavity 120, the heat transfer plate 110, the spacer 140, and/or the cover plate 130. The TCFHE 100 may also comprise a plurality of inlet ports 150 and/or a plurality of outlet ports 160.

In a specific, embodiment, the inlet port 150 and/or the outlet port 160 may be used to transport heat to and/or from the TCFHE 100. For example, the inlet port 150 may be coupled to a compressor, a pump, a fan, a blower, or the like using an inlet tubing. For example, a GAST model 1LAA-10-M100X air compressor, which provides an air flowrate of 0.85 cubic feet per minute (cfm) at a pressure of 50 pounds per square inch (psi), may be used, which occupies a volume of 561 cubic inches (8.58 inches high, 5.63 inches wide, and 11.62 inches long), weighs 17 pounds, and consumes 120 W. While the compressor, pump, fan, blower, or the like may be quite large, the closed circuit nature of the tubing and cavity 120 allow the compressor, pump, fan, blower, or the like to be located away from the TCFHE 100. For example, the compressor, pump, fan, blower, or the like may be at least about 6 inches, at least about 2 feet, or at least about 10 feet away from the TCFHE 100. Additionally or alternatively, the outlet port 160 may be coupled to a turbine, vacuum pump, vent, or the like using an outlet tubing. While the turbine, vacuum pump, vent, or the like may be quite large, the closed circuit nature of the tubing and cavity 120 allow the turbine, vacuum pump, vent, or the like to be located away from the TCFHE 100. For example, the compressor, a pump, a fan, a blower, or the like may be at least about 6 inches, at least about 2 feet, or at least about 10 feet away from the TCFHE 100. Finally, if the vacuum pump produces sufficient suction, the inlet port 150 may simply be coupled to a vent, which may be located at the inlet port 150 or remotely located away from the TCFHE 100.

The various TCFHE 100 components may be made of any materials suitable for the purposes described herein. Specifically, the TCFHE 100 components may be made of metal, plastic, composites, ceramics, multi-layer materials, or combinations thereof. It may be considered desirable for the some components, such as the heat transfer plate 110, to act as thermal conductors and thus have a relatively high thermal conductivity. For example, one of more of the materials may have a thermal conductivity of at least about 1 Btu/hr ft ° F., at least about 10 Btu/hr ft ° F., or at least about 100 Btu/hr ft ° F. Additionally or alternatively, it may be considered desirable for the some components, such as the cover plate 130, to act as thermal insulators and thus have a relatively low thermal conductivity. For example, one of more of the materials may have a thermal conductivity of no more than about 50 Btu/hr ft ° F., no more than about 5 Btu/hr ft ° F., or no more than about 0.5 Btu/hr ft ° F.

The fluid may be any substance suitable for exchanging heat with the heat transfer plate 110 and/or the thermal load 170. For example, the fluid may comprise air, nitrogen, oxygen, Freon, water, or other gases or liquids. In some embodiments, it may be desirable for the fluids to exhibit low reactivity, especially at high temperatures. In such cases, noble gases or other fluids with low reactivity may be used. The fluid may be a gas or a liquid prior to entry into the cavity 120. In some embodiments, the fluid may undergo a state change (e.g. between a liquid and a gas) due to the heat transfer within the cavity 120. Generally, the fluid will be pressurized prior to entry into the cavity 120. For example, the fluid may have a pressure of at least about 10 psi, at least about 50 psi, at least about 100 psi, or at least about 500 psi prior to entry into the cavity 120. Additionally or alternative, the fluid may have a negative pressure (e.g. down to negative 14.7 psi) upon exiting the cavity 120. While the fluid may be at an ambient temperature, the fluid may also be cooled or heated prior to entry into the cavity 120. For instance, the fluid may be hot air or an exhaust gas produced by internal or external fuel combustion, or a cold air or gas produced by a refrigeration system. While the fluid may flow intermittently through the cavity 120, the fluid will typically flow continuously through the cavity 120 from the inlet port 150 to the outlet port 160.

The heat transfer properties described herein may be dependent on the flowrate, velocity, and/or residence time of the fluid. For example, the fluid flowrate may be at least about 0.1 cfm, at least about 0.4 cfm, at least about 0.7 cfm, or at least about 1 cfm. The fluid velocity may be related to the volumetric flowrate through the cavity 120 by the cross-sectional area of the cavity (e.g. width and thickness). As such, the fluid velocity through the cavity 120 may be at least about 20 feet per second (fps), at least about 100 fps, at least about 300 fps, or at least about 450 fps. In addition, the fluid residence time may be related to the volumetric flowrate by the volume of the cavity. As such, the fluid residence time may be no more than about 5 milliseconds (ms), no more than about 1 ms, or no more than about 0.1 ms.

In an embodiment, the TCFHE 100 operates to exchange heat between the thermal load 170 and the fluid. Specifically, the fluid may be compressed in a compressor, pump, or the like, and is transported to the inlet port 150 via an inlet tubing or line. The fluid flows through the inlet port 150 and may be distributed across the cavity 120 using an inlet manifold, if the TCFHE 100 is so equipped. The heat transfer plate 110 may be in direct contact or integrated with the thermal load 170, and as such may exchange heat with the thermal load 170. The fluid then flows though the cavity 120 towards the outlet port 160. In doing so, the fluid is in direct contact with the heat transfer plate 110, and as such exchanges heat with the heat transfer plate 110, and consequently the thermal load 170. Alternatively, the fluid may be in direct contact with the thermal load 170 such that no heat transfer plate 110 exists. The fluid may then be collected in an outlet manifold if the TCFHE 100 is so equipped. The fluid may then exit the outlet port 160 and be vented or transported to another location via an outlet line and vented elsewhere.

FIG. 2 illustrates a cross-section view of another embodiment of a TCFHE 200, which may be useful when the thermal load is a fluid. The TCFHE 200 may comprise a heat transfer plate 210, a first cover plate 230, a second cover plate 232, a first spacer 240, a second spacer 242, a first inlet port 250, a second inlet port 252, a first outlet port 260, and a second outlet port 262. These components of the TCFHE 200 may be configured as shown in FIG. 2, and are substantially similar to the corresponding components described above. As such, a first cavity 220 may be maintained between the heat transfer plate 210 and the first cover plate 230, and a second cavity 220 may be maintained between the heat transfer plate 210 and the second cover plate 232.

Each side of the TCFHE 200 may operate substantially as described above. Specifically, a first fluid may flow through the first cavity 220, and a second fluid may flow through the second cavity 222. The first and second fluids may exchange heat with the heat transfer plate 210. As such, the first and second fluids may heat or cool each other, as appropriate. The first fluid and the second fluid may flow in concurrent directions as shown in FIG. 2. Alternatively, the first fluid and the second fluid may flow in counter-current directions. In some embodiments, the dimensions and geometry of the first cavity 220 may be substantially the same as the dimensions and geometry of the second cavity 222. Such may be the case when the properties of the first fluid are comparable to the properties of the second fluid. Alternatively, the dimensions and geometry of the second cavity 222 may be substantially different from the dimensions and geometry of the first cavity 220. Such may be the case when the properties of the first fluid are substantially different from the properties of the second fluid, e.g., when the first fluid is water and the second fluid is air. In such a case, one or both of the cavities may have a disrupted boundary layer.

FIGS. 3A, 3B, and 3C illustrate another embodiment of a TCFHE 300. The TCFHE 300 may comprise a heat transfer plate 310, a cover plate 330, a spacer 340, an inlet port 355, an outlet port 365, and a thermal load 370. These components of the TCFHE 300 may be configured as shown in FIGS. 3A, 3B, and 3C, and are substantially similar to the corresponding components described above. As such, a cavity may be maintained between the heat transfer plate 310 and the cover plate 330, the width, length, and/or thickness of which may be defined by the spacer 340. In addition, the thermal load 370 may be a resistor, transistor, IC, or similar heat-generating electrical component, and as such may contain electrical connections 372, such as wires, and held in place using a screw or similar connector. The TCFHE 300 may also comprise an inlet sensor port 350, an outlet sensor port 360, an inlet manifold 312, and outlet manifold 314, and a plurality of connectors 390. These components of the TCFHE 300 may also be configured as shown in FIGS. 3A, 3B, and 3C, and are described in greater detail below.

The inlet manifold 312 and the outlet manifold 314 are shown in FIG. 3C. The inlet manifold 312 may be any apparatus or device that aids in the diffusion of the fluid from the inlet port 355 into the cavity. Similarly, the outlet manifold 314 may be any apparatus or device that aids in the collection of the fluid from the cavity into the outlet port 365. The inlet manifold 312 and the outlet manifold 314 may be machined or drilled into the heat transfer plate 310, the cover plate 330, the spacer 340, or combinations thereof. In addition, the inlet manifold 312 and the outlet manifold 314 may be substantially parallel to one another and substantially perpendicular to the cavity, the heat transfer plate 310, and/or the cover plate 330. While the inlet manifold 312 may be substantially similar to the outlet manifold 314 in size, geometry, and configuration (as shown in FIG. 3C), it is also envisioned that the inlet manifold 312 may not be substantially similar to the outlet manifold 314 in size, geometry, and/or configuration.

Conditions at the inlet manifold 312 and the outlet manifold 314 may be monitored using the optional inlet sensor port 350 and the outlet sensor port 360, respectively. The inlet sensor port 350 may be substantially similar to the inlet port 355, but configured to connect to various sensors instead of allowing for the flow of fluid into the cavity. Similarly, the outlet sensor port 360 may be substantially similar to the outlet port 365, but configured to connect to various sensors instead of allowing for the flow of fluid into the cavity. Examples of such sensors may include temperature sensors, pressure sensors, composition sensors, physical state sensors, and the like. Such sensors may be located in or near the inlet sensor port 350 and the outlet sensor port 360. Alternatively, the inlet sensor port 350 and the outlet sensor port 360 may be configured to withdraw a small amount of fluid from their respective locations, transport the fluid to another location where it may be tested by the aforementioned sensors. The inlet sensor port 350 and the outlet sensor port 360 may be plugged when not in use, if desired.

The connectors 390 may be any connectors suitable for holding the heat transfer plate 310, the spacer 340, and/or the cover plate 330 in place. For example, the connectors 390 may be screws, staples, nails, clamps, adhesives, welds, other components, or combinations thereof. The connectors 390 may be positioned around the periphery of the TCFHE 300 as appropriate, for example one connector 390 at each corner. Additionally or alternatively, the connectors 390 may be positioned in the central region of the TCFHE 300 as appropriate.

FIGS. 4A, 4B, and 4C illustrate another embodiment of a TCFHE 400, which may be useful for exchanging heat with relatively small thermal loads. The TCFHE 400 may comprise a cover plate 430, a plurality of spacers 432, an inlet port 450, a plurality of outlet ports 460, a thermal load 410, a substrate 415, and a plurality of connectors 490. These components of the TCFHE 400 may be configured as shown in FIGS. 4A, 4B, and 4C. The cover plate 430, inlet port 450, thermal load 410, and connectors 490 are substantially similar to the corresponding components described above. The substrate 415 may be any surface or device that supports the thermal load 410 and/or the TCFHE 400. For example, the substrate 415 may be a PCB. In such a case, the thermal load 410 may be an IC, such as a ball grid array (BGA) IC mounted on the PCB, which is shown in FIGS. 4A, 4B, and 4C.

Unlike the other embodiments of the TCFHE described above, the spacers 432 in TCFHE 400 are integrated into and project from the cover plate 430. Specifically, the spacers 432 are configured to maintain a cavity between the thermal load 410 and the cover plate 430. If the spacers 432 contact the thermal load 410, then the height of the spacers 432 may be about equal to the cavity thickness. Alternatively, if the spacers 432 contact another surface, such as the substrate 415, then the height of the spacers 432 may be equal to the height of the thermal load 410 above the substrate 415 (e.g. allowing for solder or anything else that raises the height of the thermal load 410) plus the thickness of the cavity. In addition, unlike the other embodiments of the TCFHE described above, the outlet ports 460 in TCFHE 400 are the horizontal areas between the spacers 432. Thus, the TCFHE 400 may operate by flowing the fluid from the inlet port 450 directly onto the thermal load 410, through the cavity between the cover plate 430 and the thermal load 410, and out the four outlet ports 460. Although the outlet ports 460 in the TCFHE 400 are shown as vents, it is contemplated that the outlet ports 460 could be configured to couple to at least one outlet tubing and transport the fluid away from the TCFHE 400.

FIGS. 5A, 5B, and 4C illustrate another embodiment of a TCFHE 500, which may be useful in exchanging heat with relatively large thermal loads. The TCFHE 500 may comprise a thermal load 570, a heat transfer plate 530, a spacer 540, a distribution plate 510, an inlet port 550, an outlet port 560, a gasket 545, a cover plate 532, and a plurality of connectors 590. These components of the TCFHE 500 may be configured as shown in FIGS. 5A, 5B, and 5C. The thermal load 570, heat transfer plate 530, spacer 540, inlet port 550, outlet port 560, cover plate 532, and connectors 590 are substantially similar to the corresponding components described above. The gasket 545 may be optional and may provide a seal between the cover plate 532 and the distribution plate 510. In embodiments, the gasket 545 may be a thin layer of grease, oil, or similar material. The distribution plate 510 may be any device or apparatus that distributes the fluid to multiple locations prior to contacting the heat transfer plate 530. Specifically, the distribution plate 510 may distribute the fluid such that each flowpath (e.g. each distribution location) of the fluid is exposed to a length of the heat transfer plate 530 that is less than the total length of the heat transfer plate 530. Additionally or alternatively, the distribution plate 510 may distribute the fluid such that the fluid flows across the heat transfer plate 530 in a plurality of directions, which may include substantially counter-current and substantially orthogonal. In some embodiments, the geometry of the holes and/or distribution plate 510 may be varied. For example, the holes may be round, triangular, rectangular, or any other geometry. In addition, the distribution plate 510 may comprise a plurality of holes in an alternative geometry, for example six holes arranged in a hexagonal array, wherein each hole emits a portion of the overall fluid, e.g. one-sixth of the fluid for the hexagonal array embodiment.

In a specific embodiment best seen in FIGS. 5B and 5C, the distribution plate 510 comprises an inlet manifold 519, a plurality of inlet channels 518, a plurality of inlet sub-channels 512, a plurality of outlet sub-channels 513, a plurality of outlet channels 517, and an outlet manifold 516, all of which are in fluid communication with each other as shown in FIGS. 5B and 5C. As shown in FIG. 5B, the inlet sub-channels 512 and the outlet sub-channels 513 extend substantially across the width of the distribution plate 510, are configured substantially parallel to each other, and are configured substantially perpendicular to the flowpath of the fluid (indicated by the arrows in FIGS. 5B and 5C). As shown in FIG. 5C, the inlet sub-channels 512 extend through the distribution plate 510 into the inlet channels 518. Similarly, the outlet sub-channels 513 extend through the distribution plate 510 into the outlet channels 517. Thus, the fluid enters the inlet port 550, is distributed by the inlet manifold 519 and the inlet channels 518, travels though the distribution plate 510 via the inlet sub-channels 512, and contacts the heat transfer plate 530. After contact with the heat transfer plate 530, the fluid enters the outlet sub-channels 513, travels through the distribution plate 510 to the outlet channels 517, is collected by the outlet manifold 516, and exits via the outlet port 560. Such a configuration allows the distribution plate 510 to distribute the fluid to a plurality of locations such that the length of the heat transfer plate 530 that each flowpath of the fluid contacts is less than the total length of the heat transfer plate 530.

FIGS. 6A, 6B, and 6C illustrate another embodiment of a TCFHE 600, which may be useful for PCBs. The TCFHE 600 may comprise a thermal load 670, a heat transfer plate 615, a spacer 610, a distribution plate 620, an inlet port 650, an outlet port 660, a gasket 640, a cover plate 630, and a plurality of connectors 690. These components of the TCFHE 600 may be configured as shown in FIGS. 6A, 6B, and 6C. The thermal load 670, heat transfer plate 615, inlet port 650, outlet port 660, gasket 640, cover plate 630, and connectors 690 are substantially similar to the corresponding components described above. The thermal load 670 may be secured to the TCFHE 600 using another connector 672. The spacer 610 and distribution plate 620 may be configured as shown in FIGS. 6B and 6C, but are otherwise may be substantially similar to the corresponding components described above. Specifically, the spacer 610 comprises two cavities 612 and the distribution plate 660 comprises an inlet manifold 622 and an outlet manifold 623. In a specific embodiment, the heat transfer plate 615, spacer 610, distribution plate 620, gasket 640, and/or cover plate 630 may be integrated into a single substrate, such as a multi-layer laminated PCB. In such a case, the PCB could be configured to provide cooling to any components that produce heat, and may comprise certain areas 616 having reduced thermal resistance as compared with the remainder of the PCB (e.g. a metallic area or the like). In some case, such a PCB may provide sufficient cooling to remove the need for heat sinks and/or cooling fans. Finally, it will be appreciated that the TCFHE may be integrated into a PCB in any of the embodiments described herein, not just the embodiment shown in FIGS. 6A, 6B, and 6C.

The cavity 612 shape may be configured to provide an optimized or improved flow path, which may improve the heat transfer performance of the TCFHE 600. For example, the cavity 612 and/or spacer 610 may be configured such that the connector 672 does not extend through the cavity 612, where it could potentially change the thickness of the cavity by bending one or more of the heat transfer plate 615 and the distribution plate 620. Additionally, the cavity structure may be adjusted or aligned with the PCB's structure or design to provide cooling to specific components, which may require more cooling than other parts or components of the PCB. For example, the cavity 612 thickness may be thicker in areas where cooling is not required and thinner in areas where cooling is required. Such an embodiment may provide the heat transfer effects described herein with reduced pressure requirements. The cavity structure may be adjusted, for instance by adjusting the size or shape of the inlet manifold 622, cavities 612, and/or outlet manifolds 623 to allow the fluid to flow among areas where electronic components are located and avoid other empty or non-crucial areas on the PCB. Targeting specific paths or components of the PCB and aligning the fluid flow path accordingly, may further improve the heat transfer rate, and hence heat transfer efficiency, for such paths or components.

FIGS. 7A, 7B, and 7C illustrate another embodiment of a TCFHE 700, which may be useful for exchanging heat with relatively small thermal loads. The TCFHE 700 may comprise an alternating pressure source 780, a cover plate 730, a plurality of spacers 732, an inlet port 750, a plurality of outlet ports 760, a thermal load 710, a substrate 715, a backer plate 720, and a plurality of connectors 790. These components of the TCFHE 700 may be configured as shown in FIGS. 7A, 7B, and 7C. The cover plate 730, spacers 732, inlet port 750, outlet ports 760, thermal load 710, substrate 715, and connectors 790 are substantially similar to the corresponding components described above, and in a specific embodiment, substantially similar to the corresponding components described in conjunction with the TCFHE 400. The backer plate 720 may be any device or apparatus that provides support for the substrate 715 and/or mates with the connectors 790. The alternating pressure source 780 may be any device or component that provides alternating pressures pulses, such as positive pressure and a vacuum. A specific example of an alternating pressure source 780 is an acoustic modulator, such as a speaker.

The TCFHE 700 operates by alternating the fluid flow directions. Specifically, when the alternating pressure source 780 operates in a first direction (e.g. generating positive pressure), the fluid flows from the alternating pressure source 780, through the inlet port 750, through the cavity between the cover plate 730 and the thermal load 710, and out of the outlet ports 760. When the alternating pressure source 780 operates in a second direction (e.g. generating negative pressure), the fluid flows from the outlet ports 760, through the cavity between the cover plate 730 and the thermal load 710, through the inlet port 750, and into the alternating pressure source 780. As such, the alternating pressure source 780 may cause the fluid to exchange heat with the thermal load 710 in an alternating manner. Thus, the alternating pressure source 780 may substitute for using a compressor or other pressurized fluid sources for providing fluid flow to cool the thermal load 710. Removing such requirements may add portability and reduce maintenance for the TCFHE 700.

FIGS. 8A, 8B, 8C, and 8D illustrate another embodiment of a TCFHE 800, which may be useful when the thermal load is a fluid or solid. The TCFHE 800 may comprise a cover plate 810, a plurality of spacers 840, a plurality of sealing elements 832, a heat transfer plate 815, a plurality of inlet ports 850, and a plurality of outlet ports 860. These components of the TCFHE 800 may be configured as shown in FIGS. 8A, 8B, and 8C. The cover plate 810, spacers 840, heat transfer plate 815, inlet ports 850, and outlet ports 860 are substantially similar to the corresponding components described above, with the exception that the cover plate 810, spacers 840, and heat transfer plate 815 are cylindrical instead of planer (e.g. they may be pipes, tubes, hoses, or the like). In a specific embodiment, the heat transfer plate 815 could be a cylinder in an internal combustion engine or any other engine part. Alternatively, the heat transfer plate 815 could be part of a furnace. The sealing element 832 is analogous to the connectors described above, and may be a gasket, wedge, weld, or any other suitable apparatus for maintaining the connectivity of the other components. The thermal load for the TCFHE 800 may flow though the heat transfer plate 815. In some embodiments, the TCFHE 800 may comprise inlet and/or outlet manifolds to improve the distribution and/or collection of the fluid within the cavity.

FIG. 9 illustrates a plurality of TCFHEs 922 implemented in an enterprise system 900, for example to exchange heat with a plurality of thermal loads. Specifically, the enterprise system 900 may comprise a compressor 910, a plurality of enterprise-level quality regulating devices 912, an equipment inlet manifold 914, a plurality of equipment 916, an equipment outlet manifold 926, and a muffler 928. The equipment 916 may comprise a plurality of equipment-level quality regulating devices 918, a TCFHE inlet manifold 920, a plurality of TCFHEs 922, and a TCFHE outlet manifold 924. These components may be coupled as shown in FIG. 9 using hoses, tubes, pipes, or the like. The TCFHEs 922 may be coupled to the thermal loads described herein, and may be any of the TCFHEs described herein and/or defined by the claims. In embodiments, the TCFHEs 922 may substitute for other heat exchangers, such as heat sinks and/or fans, which may be noisy or produce undesirable sounds in the building. The equipment inlet manifold 914, TCFHE inlet manifolds 920, TCFHE outlet manifolds 924, and equipment outlet manifolds 926 allow the fluid to be distributed and collected throughout the enterprise system 900, and may be similar to the inlet and outlet manifolds described herein. The quality regulating devices 912 and 918 may comprise pressure regulators, oil traps, water traps, filters (e.g. 40 micron air filters), and/or the like. The enterprise system 900 may use any of the aforementioned fluids, for example air.

In an embodiment, the compressor 910, enterprise-level quality regulating devices 912, and/or the muffler 928 may be placed outside an enterprise building. In such a case, the heat exchanged with the thermal loads may be transported from outside and/or out of the building, as opposed to simply being drawn from inside and blown around the building, where it is heated or cooled, as appropriate, by a heating, ventilation, and air conditioning (HVAC) system. By transporting the fluid into and/or out of the building, the HVAC load (and therefore cost) associated with the building may be reduced. Moreover, the noise level in the building may be reduced by removal of the fans typically associated with exchanging heat with the thermal loads. Furthermore, after exchanging heat with the thermal load, the fluid could be transported to another portion of the building or another building to heat or cool the other building as appropriate. It will be appreciated that while FIG. 9 is described in relation to a building, the concepts described herein are equally applicable to other enclosed structures, such as automobiles, ships, submarines, aircraft, spacecraft, and any other vehicles. Moreover, it will be appreciated that the building and/or equipment described herein may be smaller-scale enclosures, such as a personal computer, a notebook computer, one or a plurality of server computers, a room, or the like.

The TCFHE described herein may be superior to existing heat sinks and fans in many ways. For example, a commercial Wakefield 623 heat sink occupies a volume of about 6.57 cubic inches and can provide a thermal resistance of about one ° C./W, but which requires a fan generating an air velocity of about 8 fps. A commercial EBM-Papst 4312 fan that can provide about 11 fps air velocity (or a flowrate at about 55.9 CFM) may be used with the Wakefield 623 heat sink. However, the fan occupies a volume of about 27.71 cubic inches, weights about 0.49 pounds, and consumes about 1.2 W. Hence, combining such commercial heat exchangers may not be practical for micro and macro scale technologies. On the other hand, the prototype TCFHE with a cavity at about three mils in thickness may provide about the same thermal resistance (about 1° C./W) with a flowrate of air at about 0.7 CFM and a pressure at about 49 psi. In addition, the TCFHE allows the fluid source and/or destination to be remotely located with respect to the location where heat exchange occurs, which allows the actual heat exchanger to be relatively small and creating a significant packaging advantage.

EXAMPLES

A plurality of experiments were conducted to further explore the concepts described herein. The test apparatus similar to that illustrated and described in conjunction with FIG. 3 was used. The heat transfer plate and the cover plate were made of black anodized aluminum and were each 1.5 inches square. The heat transfer plate was 0.25 inches thick and the cover plate was 0.125 inches thick. The heat transfer plate had four #10-32 threaded holes for the inlet and outlet ports as well as the inlet and outlet sensor ports, all of which were equipped with barbed fittings. The inlet and outlet sensor ports only contained pressure sensors for the experiments. The heat transfer plate also had inlet and outlet manifolds that were 1 inch wide, 0.125 inches thick, and 0.125 inches long. The spacer provided a cavity that was 1.25 inches wide and 1 inch long. Spacers of various thicknesses were used to modify the thickness of the cavity. Paper spacers were used to create cavity thicknesses of 20 mils, 10 mils, 5 mils, and 3 mils, while Kapton polyimide was use to create cavity thicknesses of 2 mils and 1 mil. The apparatus was held together using four #4-40 screws. The thermal load was a TO-220 power transistor (IRL3803 MOSFET), and a TO-220 (LM 35) temperature sensor was mounted adjacent to the thermal load to monitor the outside surface temperature of the heat transfer plate. The entire apparatus was thermally insulated in bubble wrap and silicone foam material.

A commercial air compressor was remotely located and connected to the prototype using 0.25-inch outer diameter (0.18-inch inner diameter) air hoses and fittings. The air compressor provided up to 1.2 cfm of air at up to 60 psi. The hose connected to the inlet port was also connected to a pressure regulator, a flowrate sensor, and a temperature sensor to regulate the pressure, flowrate, and temperature of the air at the inlet. The hose connected to the outlet port was connected to another temperature sensor to monitor the temperature of air at the outlet. Two additional hoses were used to connect the inlet and outlet sensor ports to monitor the pressure of the flow at the inlet, the outlet, and across the cavity. The flowrate sensor is configured to measure the flowrate of pressurized air up to about 50 psi, while the pressure sensors are configured to measure the pressure of air up to about 29 psi. Therefore, when the flowrate and pressure exceed the measurement limits of the flowrate sensor and the pressure sensors, measurements are obtained using manual flow meters and pressure gauges, respectively. As shown in FIG. 10, the test apparatus was monitored by a PCB and test software capable of downloading the results into an EXCEL file. A load power of 3.606 W was used in the experiments.

At a cavity thickness of 3 mils, the apparatus produced a thermal resistance of 1.2° C./W using an air flowrate of 0.7 cfm, an inlet pressure of 49 psi, and an outlet pressure of 4 psi. As such, the air velocity within the cavity was 305 miles per hour (about 448 fps), and required 7 W of pneumatic power. Lower thermal resistances could be obtained at the expense of higher required air pressure and/or air flowrates. In addition, the air outlet temperature was about equal to the heat transfer plate external surface temperature, which indicates that lengthening the cavity may not improve heat transfer performance. However, improved heat transfer performance may be obtained by shortening the length of the cavity.

FIG. 11 illustrates a correlation between thermal resistance and air flowrate at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. According to the curves, the thermal resistance decreases as the flowrate increases, which leads to improved heat transfer performance. In addition, thermal resistance decreases as the cavity thickness decreases. Thermal resistances as low as about 1.2° C./W at a flowrate of about 0.7 CFM were obtained when the cavity thickness is about three mils.

FIG. 12 illustrates a correlation between cavity air pressure drop and air flowrate at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. According to the curves, the cavity pressure drop increases as the air flowrate increases. In addition, the pressure drop across the cavity increases as the thickness of the cavity decreases. The highest obtained pressure drop value is obtained for the smallest thickness at about 45 psi and for a flowrate at about 0.7 CFM. Hence, the highest pressure drop coincides with the lowest obtained thermal resistance value. When such conditions are met, the heat transfer performance may be optimized for a given configuration.

FIG. 13 illustrates a correlation between thermal resistance and pneumatic power at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. The pneumatic power in watts was calculated according to the formula:

Pneumatic Power (W)=(1000*226*inlet pressure (psi)*flowrate (cfm))

According to the curves, the thermal resistance decreases as the pneumatic power increase. In addition, the curves show that thermal resistance decreases as the cavity thickness decreases.

FIG. 14 illustrates a correlation between load temperature and air flowrate at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. According to the curves, the load temperature decreases as air flowrate increases. In addition, the load temperature decreases as cavity thickness decreases. Further, a minimum load temperature is obtained at about 30° C. for the smallest thickness when the flowrate is at about 0.7 CFM. This minimum load temperature coincides with the optimized conditions, discussed above, for improved heat transfer performance. Moreover, such data shows that the thermal load can be cooled to close to the inlet air temperature (about 29° C.).

FIG. 15 illustrates a correlation between air outlet temperature and load temperature at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. According to the curves, the air outlet temperature increases as the load temperature increases. Interestingly, the relationship is fairly independent of cavity thickness with only a slight increase in air outlet temperature for smaller cavity thicknesses.

FIG. 16 illustrates a correlation between cavity air velocity and air flowrate at various cavity thicknesses. The air had an inlet temperature of about 29° C., and air flowrates were measured using a manual rotameter above 0.4 cfm and an electronic flowmeter below 0.4 cfm. As such, there is a discontinuity in the curves at about 0.4 cfm. According to the curves, the cavity air velocity increases as the air flowrate increases. In addition, the cavity air velocity increases as the cavity thickness decreases.

Based on the analysis above, the heat transfer performance may be improved by reducing the thickness of the cavity at the expense of increasing the pressure of the flow of fluid inside the cavity. Additionally or alternatively, the heat transfer performance may be improved by reducing the residence time, the flow distance, or both inside the cavity. This may be accomplished by reducing the cavity length or modifying the cavity path. For instance, at least one manifold may be added to the TCFHE to control the flow path through the cavity. Additionally, the shape of the manifold may be convoluted to achieve better control.

At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R₁, and an upper limit, R_(u), is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. The discussion of a reference in the disclosure is not an admission that it is prior art, especially any reference that has a publication date after the priority date of this application. The disclosure of all patents, patent applications, and publications cited in the disclosure are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to the disclosure.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. 

1. A heat exchanger comprising: a first surface; a second surface; and a spacer configured to maintain a cavity between the first surface and the second surface, wherein the cavity has a thickness less than or equal to about 20 thousands of an inch (mils) and has a width-to-thickness ratio greater than or equal to about 8:1, and wherein the cavity allows any fluid in the cavity to exchange heat with the first surface, the second surface, or both.
 2. The heat exchanger of claim 1, wherein the cavity has a thickness of less than or equal to about three mils.
 3. The heat exchanger of claim 1, wherein the first surface comprises a cover plate and the second surface comprises a heat transfer plate.
 4. The heat exchanger of claim 1, wherein the first surface comprises a cover plate and the second surface comprises a thermal load.
 5. The heat exchanged of claim 1, wherein the spacer defines a plurality of cavities.
 6. The heat exchanger of claim 1, further comprising a fluid distribution plate.
 7. The heat exchanger of claim 1 further comprising: an inlet port coupled to the first surface, the second surface, the spacer, or combinations thereof; and an outlet port coupled to the first surface, the second surface, the spacer, or combinations thereof, wherein the inlet port, the cavity, and the outlet port allow any fluid to flow into the inlet port, through the cavity, and out of the outlet port.
 8. The heat exchanger of claim 7 further comprising: an inlet manifold connected to the inlet port and located on the first surface, the second surface, the spacer, or combinations thereof; and an outlet manifold connected to the outlet port and located on the first surface, the second surface, the spacer, or combinations thereof.
 9. The heat exchanger of claim 1 further comprising an alternating pressure source coupled to the first surface and in fluid communication with the cavity, and wherein the inlet port, the cavity, and the outlet port allow the fluid to reverse directions as the alternating pressure source alternates.
 10. The heat exchanger of claim 1, wherein the first surface and the second surface are substantially concentric cylinders, and wherein the spacer is a ring.
 11. The heat exchanger of claim 1, wherein the heat exchanger does not comprise any fins.
 12. An apparatus comprising: a thermal load; and a heat exchanger substantially adjacent to or integrated with the thermal load, wherein any fluid flowing through the heat exchanger has a velocity greater than or equal to about 20 feet per second (fps).
 13. The apparatus of claim 12, wherein the fluid has a velocity greater than or equal to about 300 fps.
 14. The apparatus of claim 12 further comprising: an exhaust tubing having a proximate end and a distal end, the proximate end coupled to the heat exchanger; and a vent coupled to the distal end, wherein the exhaust tubing is configured to transport heat away from the thermal load.
 15. The apparatus of claim 12 further comprising: a compressor or a pump; and an inlet tubing coupled to the compressor or pump and the heat exchanger.
 16. The apparatus of claim 12, wherein the heat exchanger comprises a fluid cavity having a volume less than or equal to about 0.01 cubic inches.
 17. The apparatus of claim 12, wherein the heat exchanger has a thermal resistance less than or equal to about 2° Celsius per Watt (° C./W).
 18. The apparatus of claim 12, wherein the apparatus is a building, a room, a computer, a vehicle, a ship, a submarine, an aircraft, or a spacecraft.
 19. The apparatus of claim 11 comprising a printed circuit board coupled to the thermal load.
 20. A heat exchanger configured to implement a method comprising: passing a fluid having a first temperature through a cavity a least partially defined by a surface having a second temperature, wherein the cavity substantially reduces or eliminates the heat transfer boundary layer of the fluid.
 21. The heat exchanger of claim 20, wherein the cavity has a thickness less than or equal to about 10 thousands of an inch (mils).
 22. The heat exchanger of claim 20, wherein the fluid has a residence time in the cavity less than or equal to about five milliseconds (ms). 